A story telling element in many forms of fiction, usually a story produced by a large, soulless studio or was never thought out that much in the first place, that means
Love
Interest
Non-
Essential
To
Story
meaning a character that has little to no personality or backstory in the plot and whose only purpose is to be a nice compliment to the protagonist.
This phrase was first coined by the Nostalgia Chick in her review of Dragonheart.